Call handling for ims registered user

ABSTRACT

The present invention proposes a solution for providing IMS services to users having circuit-switched controlled terminals. In particular, it is proposed, in order to allow IMS to take the full call and service control, to combine circuit-switched and packet-based multimedia functionality in a new node type called Mobile Access Gateway Control Function (MAGCF). In particular the present invention provides a method for ensuring that the MAGCF node acts as a roaming anchor point in order to enforce the handling of originating and terminating calls in the IMS.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to performing call handling for a userhaving circuited-switched controlled user's equipment and being portedto a IMS domain.

BACKGROUND

Third Generation (3G) Networks such as UMTS (Universal TelecommunicationNetwork) and CDMA 2000 provide high-speed wireless Internet access tomobile users over a wide coverage area. For the 3G networks the IPMultimedia Subsystem IMS has been defined to provide cellular access tothe services of the Internet in order to support telephony andmultimedia services. The IMS uses packet-switched technology, inparticular IP-network and other IETF protocols for provision ofservices. The 2nd Generation networks, like GSM, provide voice based ona circuit-switched technology. The strength of IMS is the provision ofenhanced Services, for example multimedia services combining voice anddata. Further, the usage of IP-network as a single underlying standardallows an easy and fast service deployment.

A Session Initiation Protocol SIP has been chosen in IMS for signallingbetween the user's equipment UE and the IMS as well as between thecomponents within the IMS. The IMS uses SIP also to complete voice andmultimedia calls in the Internet. In order to be able to use the IMSservice, the communicating user's equipment has to support IMS, whichmeans SIP has to be implemented in the user's equipment.

In the following simplified network architectures of IMS is described.In particular the nodes being involved in provision of service in IMSarchitecture are mentioned.

The components of the IMS system are the Call Session Control Function(CSCF), the Media Gateway (MGW)/Media Gateway Control Function (MGCF),the Home Subscriber Register (HSR), the Application Server (AS).

The CSCF acts as a call server and handles call signalling, it supportsand controls multimedia sessions and performs address translationfunctions. The CSCF can be functionally decomposed to S-CSCF, I-CSCF andP-CSCF. The Proxy-CSCF (P-CSCF) is the first contact point in a IMSnetwork and it provides authorization of bearer resources, further itforwards a SIP register request received from the User Equipment UE toan I-CSCF determined using the home domain name, as provided by theuser. In the opposite direction it forwards the SIP request or responseto the UE. Moreover the CSCF forwards SIP messages received from the UEto a SIP server (S-CSCF) whose name the P-CSCF has received as a resultof the registration procedure.

The Interrogating-CSCF (I-CSCF) is the contact point within anoperator's network for all connections destined to a subscriber of thatnetwork operator, or a roaming user currently located within thatnetwork operator's service area. There may be multiple I-CSCFs within anoperator's network. The main function performed by the I-CSCF isassigning a S-CSCF to a user performing SIP registration.

The Serving Call Session Control Function (S-CSCF) is the node thatperforms the session management for the IMS network. There can beseveral S-CSCFs in the network. The main functions of S-CSCF comprise:acceptation of registration requests from UE, interacting with servicesplatforms for the support of services. Further it provides endpointswith service event related information (like for example notification oftones/announcement together with location of additional media resources,billing notification).

The Home Subscriber Register HSR is the centralized subscriber database.The HSR interfaces with the I-CSCF and the S-CSCF to provide informationabout the location of the subscriber and the subscriber's subscriptioninformation. The HSR is responsible for holding the following userrelated information: user identification, numbering and addressinginformation, user security information for authentication andauthorization. The HSR supports the user registration, and storesinter-system location information.

The IMS supports several nodes for inter-working with legacy networks,like for example Media Gateway Control Function (MGCF).

The MGCF performs protocol conversion between cellular call controlprotocols and IMS protocols. For example, the MGCF receives a SIPmessage from the CSCF and converts it into appropriate ISUP messages.Thus, the primary function of MGCF is to convert signalling informationfrom one format to another in uplink and downlink direction. In UMTSthis will predominantly be between Pulse Code Modulation (PCM) in thePSTN and an IP based format.

The IMS Access Server hosts and executes services, the user requestedfor.

As already mentioned the UMTS system allows mobiles operating in packetmode to establish voice calls using SIP as the signalling protocol. TheSIP messages are sent to communicate the request to the Call SessionControl Function (CSCF) in the IMS. In this case, the data istransmitted as packets throughout the UMTS network.

Thus, the IMS has been deployed for the 3G networks for provision ofservices using packet-switched technology with SIP as applied signallingprotocol. However, currently the major numbers of user's equipment donot support IMS technology with SIP as signalling protocol for voiceservice, since said user's equipment is adapted for a circuit-switchedcontrolled domain. Thus, for the access to the IMS an adaptation of theuser's equipment is necessary, which leads to the problem of exchangingthe end terminals.

Further problem which occurs is the provision of conversationalservices. In the IMS real time bearers are provided, which are notpossible efficiently for voice services. For efficiently providing aspeech service via GSM or WCDMA access, the circuit switched access isto be used.

SUMMARY AND DESCRIPTION OF THE INVENTION

Therefore, it is an object of the present invention to provide asolution for providing packet-switched multimedia services to user'sequipment operating in circuit-switched controlled domain.

The invention is disclosed in the independent claims.

Advantageous embodiments are described in the dependent claims beingdisclosed in the corresponding parts of the description.

The invention discloses Access Gateway Node (MAGCF) adapted to handle acall in a packet-based multimedia system domain for a circuit-switchedcontrolled user's terminal located in circuit-switched controlled domainwherein said Access Gateway Node comprises an originatingcircuit-switched logic adapted to receive an originatingcircuit-switched call either directly from the circuit-switchedcontrolled user's terminal or from a serving mobile circuit-switchedfunction serving mobile circuit-switched function by means of a routingnumber being used to route the circuit-switched call to the AccessGateway Node. Furthermore the Access Gateway Node comprises anoriginating packet-based multimedia logic adapted to send an originatingpacket-based multimedia call via an proxy call control function beingpart of the Access Gateway Node towards the packet-based multimediadomain. Furthermore terminating call functionality is includedcomprising a terminating packet-based multimedia logic adapted toreceive from the packet-based multimedia domain a terminatingpacket-based multimedia call being addressed to the proxy call controlfunction and a terminating circuit-switched logic adapted to send aterminating circuit-switched call towards the circuit-switchedcontrolled user's terminal. Furthermore there is also a conversionfunction adapted to convert the originating circuit-switched call intothe originating packet-based multimedia call and the terminatingpacket-based multimedia call into the terminating circuit-switched call.

Further the present invention discloses a method for handling a call ina packet-based multimedia domain for a circuit-switched controlleduser's terminal located in circuit-switched controlled domain. Saidmethod comprises the following steps

-   -   Performing call originating procedure comprising        -   Receiving an originating circuit-switched call either            directly from the circuit-switched controlled user's            terminal or from a serving mobile circuit-switched function            by means of a routing number being used to route the            circuit-switched call to the Access Gateway Node (MAGCF)            and,        -   Converting the originating circuit-switched call into an            originating packet-based multimedia call and,        -   Sending the originating packet-based multimedia call via an            integrated proxy call control function towards the            packet-based multimedia domain and,    -   Performing call terminating procedure comprising        -   Receiving from the packet-based multimedia domain a            terminating packet-based multimedia call being addressed to            the integrated proxy call control function, and        -   Converting the terminating packet-based multimedia call into            a terminating circuit-switched call and,        -   Sending the terminating circuit-switched call towards the            circuit-switched controlled user's terminal.

Further advantageous embodiments are described in the dependent claims.

In the following preferred examples of the present invention shall bedescribed in detail, in order to provide the skilled person withthorough and complete understanding of the invention, but these detailedembodiments only serve as examples of the invention and are not intendedto be limiting. The following description shall make reference to theenclosed drawings, in which

FIG. 1 shows a schematic representation of an architecture of AccessGateway Node according to the present invention, and

FIG. 2 shows a flowchart of an embodiment of the present invention forcall originating method being to be performed on the Access GatewayNode,

FIG. 3 shows a flowchart of an embodiment of the present invention forcall terminating method being to be performed on the Access GatewayNode,

FIG. 4 shows an embodiment of the present invention for involving MAGCFas a roaming anchor point,

FIG. 5 shows a further embodiment of the present invention for involvingMAGCF as a roaming anchor point,

FIG. 6 shows a schematic embodiment for call originating in homenetwork,

FIG. 7 shows an embodiment of a signalling sequence for call originatingin home network,

FIG. 8 shows a schematic embodiment for call originating in visitednetwork,

FIG. 9 shows an embodiment of a signalling sequence for call originatingin visited network,

FIG. 10 shows a schematic embodiment for call termination in homenetwork,

FIG. 11 shows an embodiment of a signalling sequence for callterminating in home network,

FIG. 12 shows a schematic embodiment for call termination in visitednetwork.

It should be noted that the term “entity”, “node”, “module”, “logic” inthe context of the present invention refers to any suitable combinationof hardware and software for providing a predetermined functionality inthe communication network. In this way, said terms generally refers to alogical entity that can be spread out over several physical entities,but can also refer to a physical entity located in one physicallocation, if no explicit definition is given.

It should be noted that the term “user” in the context of the presentinvention refers to circuit-switched controlled user equipment, whereinsaid user equipment is a combination of hardware and software. Howeverin the following description the terms “user” and “user terminal” shouldbe seen as having the same meaning, if it is not stated differently.

Preferably, the communication network is a mobile communication network,e.g. is a wireless communication network operating according to GSM,GPRS (General Packet Switched Radio) or UMTS (Universal Mobile TelephoneSystem) or any 3G system like for example EDGE, CDMA2000. And preferablythe packet-switched multimedia domain is the IP multimedia Subsystem(IMS).

According to the present invention it is proposed, in order to allow IMSto take the full call and service control, to combine the logicalfunctionality of a cellular switching center and the logicalfunctionality of IMS in an Access Gateway Node, which is called in thefollowing MAGCF. In particular it is proposed that this new MAGCF nodecomprises a serving circuit-switched functionality like for example MSC,or MSC-S being serving MSC for a roaming user, or a GMSC-S forterminating calls to a roaming user in a network without MAGCFfunctionality, and optionally gsmSCF for originating calls for a roaminguser and further it is proposed that the MAGCF has packet-switchedmultimedia functionality which is in particular the proxy call controlfunction, like for example the P-CSCF for forwarding SIP messages fromthe user to IMS and from IMS to the user. In general it might be saidthat the MAGCF handles in the packet-switched multimedia domain onbehalf of the user with a circuited-switched terminal. Further it isproposed that the MGCF performs protocol conversion between cellularcall control protocols and IMS protocols. The task of an integrated useragent is to fulfil the IMS functionality and to handle on behalf of theuser.

The basic concept is to ensure that the MAGCF handles all originatingand terminating calls or in other words, it is to be ensured that theMAGCF is the anchor point for the cellular access towards IMS.

The present invention concentrates on establishing and handling of usercalls. However, before establishing a packet-switched multimediasession, the user needs to perform registration procedure in order tolet the circuited-switched and the IMS domain know the location of saiduser. This registration is performed by means of the SIP protocol andthe user agent being part of the MAGCF and handling on behalf of theuser performs the registration.

In the following registration with MAGCF as an anchor point isdescribed. For example an embodiment is given describing changing of aservice MSC-S while roaming to a visited network. When roaming into avisited network without support for MAGCF, the last responsible MAGCF iskept as anchor point.

According to the present invention said MAGCF node has the MSCfunctionality, like MSC-S and the IMS functionality in form of useragent UA and an integrated P-CSCF. The MAGCF has therefore thecapability to communicate with the HLR and with the IMS and at least oneMAGCF is foreseen for a user in a home network. Usually in a network anumber of MSCs is provided, wherein a MSC is responsible for users beinglocated in location areas being assigned to the MSC. Changing of theresponsible MSC due to user's movement implies initiation of the roamingprocedure aiming to register the user in a new MSC and de-register fromthe old MSC by performing all the necessary updates in respect therewithin the corresponding nodes. After entering a new location area, theterminal sends a location update request to the new MSC. When receivingthis message, the MSC identifies the subscriber to be new in itsresponsibility and therefore the HLR is contacted for updating thelocation information. Upon receiving the location update message the HLRinforms the old MSC that the subscriber has roamed into a new MSC area.According to the present invention a user serving MSC might be eitherpart of a MAGCF or in case a user roams in a visited network it might bea usual MSC located in said visited network and communicating with thecircuited-switched part of the MAGCF. In both cases a message is sentfrom the HLR that the MSC does no longer serve the subscriber. In case aMSC is a part of MAGCF in this case the new MAGCF is assigned to theuser, which results in changing the address of the serving MAGCF in theS-CSCF and it results also in storing an address of the S-CSCF in theMAGCF. In case the serving MSC is not a part of the MAGCF, for exampleit might occur when a user roams in a visited network, in this case theserving MSC might change but the MAGCF remains the same. In order toregister to the IMS system, the HLR, when receiving a location update,checks whether the MSC is a part of a MAGCF or not. Further the HLRchecks the requesting subscriber. In order to provide the IMSfunctionality to the users, said users has to be ported to the IMSsystem. In other words, the user has to either announce actively thechange to the IMS system or the system might decide to port cellularusers to the IMS system. A corresponding notification about the user isto be stated in the HLR. In case a user is not ported, it is proposed toapply the standard behaviour for a cellular user like it is alreadyknown. In case the user is ported to the IMS, it is proposed that theHLR sends all the parameters, which are usually stored at the SIM cardin the user's equipment to the MAGCF. Upon receipt of the parameters theuser agent is contacted in order to register and to subscribe thesubscriber in the IMS system. Preferably the applied protocol for theregistration and for the subscription purpose is the SIP protocol, inthis case also the user agent has SIP functionality implemented. Duringthe IMS registration, the user agent acts on behalf of the subscriber.All steps necessary for registration are performed by the means of theIMS entities integrated in the MAGCF. The steps might include forexample authentication of the user which is to be authenticate. Howeverit is to be stated that the authentication is not mandatory because thesolution might rely on the fact that the user has already beenauthenticated as part of the circuit-switched access and further itmight be assumed that the MAGCF is connected to a trusted VPN. Theresult of the registration is that the MAGCF stores the S-CSCF addressand following the IMS rules for registration, the S-CSCF stores theMAGCF address where the registered subscriber can be reached, preferablythe P-CSCF address as integrated in the MAGCF is stored.

If a user roams in a visited network without MAGCF functionality then incase of roaming to a MSC, it is proposed that the current MAGCF staysresponsible for the user. In case no MAGCF is assigned to the user yetthen it is proposed to take a default MAGCF. Thus the location updateprocedure is restricted to updating an MSC in the HLR but not theresponsible MAGCF as long as the user stays in the visited network.

After the registration is finished, a session establishment procedureincluding IMS Call setup procedure is initiated.

Thus, after a successful registration the MAGCF knows the S-CSCF and theS-CSCF has the MAGCF address, in particular the P-CSCF whichfunctionality is part of the proposed MAGCF.

In the following a procedure is described according to the presentinvention how to enforce that the call handling is performed by aserving MAGCF. This situation might occur for example when roaming in aremote visited network, where no MAGCF functionality is available. Inthis case it is proposed to use the last serving MAGCF as roaminganchor.

The call handling procedure is described according to FIG. 1 presentingschematically a structure of a MAGCF being a anchor point between acircuited-switched CS network with a user's circuited-switched controlterminal MS and a packet-switched multimedia network PS. There is anoriginating circuit-switched logic, Org CS, adapted to receive anoriginating circuit-switched call. Said call might be received directlyfrom the circuit-switched controlled user's terminal in case the servingMSC is part of the MAGCF. This situation occurs when a user is in homenetwork and it is defined that the serving MSC is included in the MAGCF.Alternatively the MAGCF might receive an originating call from a servingmobile circuit-switched function, which might be for example a MSC/VLRin a visited network handling the user. In this case the calling usercontacts the MSC/VLR in a well known manner, using for example theB-number, and according to the present invention the MSC/VLR has toroute the call to the MAGCF being responsible for the user. This isensured by means of assigning a routing number. In the furtherdescription two methods for assigning a routing number are given; one isbased on a roaming number assigned to a call and identifying in a uniquemanner the MAGCF, where the call is to be routed. For the purpose ofassigning a number Intelligent Network IN-Functions are applied. In asecond method the B-number is enhanced with a prefix, which defines howto route a B-number to the MAGCF. As it is also described in accordancewith the both methods the routing number is assigned according to anindication about the Access Gateway Node serving the user received froma user's directory, like for example the HLR.

Independent whether the originating CS call is received directly fromthe user's terminal or via a MSC/VLR, in the next step the MAGCFconverts the originating CS call in the conversion unit, Conv, into anoriginating packet-based multimedia call which is past to an originatingpacket-based multimedia logic Orig PS adapted to send the originatingpacket-based multimedia call towards the packet-based multimedia domain.According to the present invention it is proposed to have a proxy callcontrol function P-CSCF being part of the Access Gateway Node. TheProxy-CSCF (P-CSCF) is the first contact point in a IMS network, itforwards a SIP messages received from the user to S-CSCF which name theP-CSCF has received as a result of the registration procedure. In theopposite direction it forwards the SIP request or response to the UE.Said P-CSCF is also used to reach the MAGCF for the call termination.Thus a terminating packet-based multimedia logic, Term PS, is proposedwhich is adapted to receive from the packet-based multimedia domain aterminating packet-based multimedia call. Said call is routed to theMAGCF by means of the address of the proxy call control function,P-CSCF. Said call is converted to a terminating circuit-switched call inconversion function, Conv, and sent towards the circuit-switchedcontrolled user's terminal by means of a terminating circuit-switchedlogic, Term CS. The termination call might be either sent directly tothe circuit-switched controlled user's terminal in case a servingcircuit-switched node is part of the circuit-switched function or it isto be routed to the serving circuit-switched node in case said servingcircuit-switched node is not a part of the circuit-switched function.

Further it is proposed that the MAGCF has a suppression function adaptedto suppress the received originating circuited-switched call fromhandling in the circuit-switched domain. This ensures that theoriginating call is really handled in the IMS domain. In order todeliver the circuited-switched call to the user it is to be ensured thatthe received terminating packet-based multimedia call is terminated inthe MAGCF.

In the following a method according to the present invention isdescribed in respect to FIG. 2 and FIG. 3. FIG. 2 presents a calloriginating case. In the first step 21 the MAGCF receives an originatingcircuit-switched call. Said call might be either received directly fromthe circuit-switched controlled user's terminal, in case a servingmobile circuit-switched function, MSC, is integrated in the MAGCF. Incase the user is handled by a separate serving mobile circuit-switchedfunction, then the call is to be routed to the serving MAGCF by means ofa routing number. The assignment of the routing number is describedfurther. In step 22 the circuited-switched call is converted into anoriginating packet-based multimedia call and sent in step 23 towards thepacket-based multimedia domain, 24. In the packet-switched multimediapart the proxy call control function P-CSCF is involved in theforwarding of the call.

FIG. 3 shows an embodiment for call termination. In step 31 aterminating packet-based multimedia call is received from thepacket-based multimedia domain. The routing of the call is performed bymeans of a proxy call control function P-CSCF. In step 32 the call isconverted into a terminating circuit-switched call and sent towards thecircuit-switched controlled user's terminal, as described above eitherdirectly or via a serving MSC/VLR.

In the following embodiments of the present inventions are given.

In the following an embodiment is described showing an assignment of arouting number in case a user roams in a visited network and is servedby a MSC/VLR being not a part of a serving MAGCF. In order to route alloriginating calls from the serving MSC/VLR to the roaming anchor MAGCF,a CAMEL mechanism as an example is used. The CAMEL approach is taken asan example and it has no restriction to the present invention.

In the following some essential features of a CAMEL network being usedin one embodiment of the present invention are mentioned. CAMEL is anetwork feature which allows the network operator to provide the mobilesubscribers with the operator specific services even when mobilesubscribers are roaming outside the home network. According to CAMELarchitecture, CAMEL Service Control Functionality (gsmSCF) functionalityis to be provided in the subscriber's home PLMN, which contains theCAMEL service logic needed to implement operator specific services.Further there is also CAMEL Service Switching Functionality (gsmSSF)taking part in the transaction handling and executing the instructionsgiven from the gsmSCF. Often used protocol for communication betweennodes in the CAMEL architecture is the CAMEL Application Part (CAP)protocol. In the frame of CAMEL, a so called Trigger Detection Point(TDP) is defined, which specifies a point of time in transactionhandling when the gsmSCF shall be contacted. When the TDP is met thegsmSSF opens a dialog to gsmSCF. There are a number of functionalitiesdefined for the gsmSCF, among other things; the gsmSCF can be providedwith information about ongoing transaction, like for example destinationaddress and duration of transaction.

Returning to the embodiment of the present invention for ensuring thatall calls are handled by a serving MAGCF, in the following two possibleapproaches for this purpose are presented. In the first solution aroaming number is used that is dynamically assigned to the call forrouting from the serving MSC/VLR to the serving MAGCF, the secondmodifies the actually dialed B-number by adding a prefix to it.

The first approach is based on the concept of using a temporary roamingnumber. This solution is described in respect to FIG. 4.

In FIG. 4 a MSC/VLR is presented, which serves a user being located inits serving area, which is A visiting network. According to the presentinvention the MSC/VLR communicates with the MAGCF being located in thehome network, A home, and comprising also gsmSCF functionality. Thus,the MAGCF provides connectivity to the circuit-switched domain. On theother hand the MAGCF provides signalling communication to the IMS and inparticular to the S-CSCF. The S-CSCF is the user serving node in the IMSdomain. It acts as a call server and handles call signalling. Further,according to FIG. 4 there is also the IMS AS which hosts and executesservices, the user requested for. The AS is for example responsible forthe call flows and user interface interactions with subscribers. The IMSAS delivers services to the IMS, such as push-to-talk, ringback tones,prepaid calling card, multimedia conferencing and multimedia messagingservice logic. Further there is also a HLR being a user database locatedin the circuit-switched network.

According to the preferred embodiment of the present invention it isproposed to perform the transmission of user plane and of the usersignalling on two independent layers. In the user plane, interworkingelements are required to convert IP based media streams accordingly. TheMedia Gateway (MGW) node is responsible for this function. TheMultimedia Resource Function Processor (MRFP) provides adjunct mediaprocessing for the application layer such as audio mixing, contentrecording and playback, codec transcoding, statistic obtaining and isconnected to the MGW. The MRFP is not dedicated to a single applicationbut provides media processing as a shared resource to a multitude ofapplications. The Media Resource Function Controller (MRFC) provides amedia resource broker function between the AS and MRFP resources in theIMS, and can be implemented as part of an application server or as aseparate network element.

According to FIG. 4 the flow of signaling information is depicted bymeans of a dotted line and the continuous line represent the flow ofuser plane.

In respect to FIG. 4 the following steps are proposed in order todeliver the call handling to the MAGCF.

When a user moves to a visited network, at first a location updateprocedure is to be performed in order to inform the HLR about the newlocation of the user. The communication between the MSC/VLR and HLR isrealised by means of a MAP protocol. Thus, the HLR receives a MAPmessage for Update Location, the HLR determines whether the sending nodesupports MAGCF functionality. This can be achieved by including anindication from the sending node that MAGCF functionality is supported.Alternatively, the HLR can check in a predefined list administered inthe HLR. If the HLR determines that MAGCF function is not supported bythe node sending Update Location, it is proposed that the HLR adds CAMELdata to the data sent via MAP operation Insert Subscriber Data. ThisCAMEL data arms the CAMEL Trigger Detection Point for “Collect_Info”,which indicates to the MSC/VLR to establish a connection to the gsmSCF,being responsible for the handling of user's call in the home network.As the address of the gsmSCF to be contacted, the HLR includes theaddress of the currently serving MAGCF, step 41. In case there is noserving MAGCF known in HLR, the HLR can use a predefined default MAGCF.As a result of the location procedure, the MSC/VLR has the contactaddress of MAGCF. In step 42 the MSC/VLR receives a call setup requestincluding the called B-number. The CAMEL Trigger Detection Point“Collect_Info” is triggered immediately upon reception of the callrequest, which results that the MSC/VLR halts call setup processing andcontacts the gsmSCF as addressed by the CAMEL subscription data receivedfrom HLR. The CAP message InitialDP is sent to the gsmSCF including theB-number. Since the HLR provided the address of the serving MAGCF asgsmSCF address, actually the MAGCF is contacted, step 43. In thesubsequent step 44, the MAGCF allocates a temporary roaming number to beused to route calls to this MAGCF. The MAGCF stores the receivedB-number, so that it can later match the incoming roaming number call tothe right B-number. In step 45 the MAGCF instructs the MSC/VLR to routethe originating call to that roaming number. The CAP message Connect issent from MAGCF to MSC/VLR. By means of the received roaming number, theserving MSC/VLR routes the hold call to the MAGCF, step 46. In step 47the MAGCF receives the call, coming in with the roaming number. TheMAGCF then looks up the originally dialed B-number, which was storedwhen allocating the roaming number. The B-number as called destinationis used in step 48 to route the call to the S-CSCF being responsible forserving the A-subscriber for execution of originating services.

Thus, the described approach ensures that an originating call initiatedin a visited network is forwarded to the MAGCF in order to be handled inthe IMS domain. The call handling is described further.

In the following a second approach is presented for routing alloriginating calls to the MAGCF node being the roaming anchor point. Thesolution is based on the concept of using a prefix to the B-number anddescribed in respect to FIG. 5. FIG. 5 comprises all nodes as disclosedin respect to FIG. 4 with the difference that the gsmSCF is depicted asa separate node. However this should not be seen as any restriction forthe protection scope of the present invention. According to the presentembodiment the gsmSCF is to be used as a database to add a specificprefix to the B-number, wherein the prefix needs to be specific for theselected MAGCF and preferably different prefixes are used for differentselected MAGCF nodes. Thus, since the gsmSCF is a central point thatadds the prefixes it is shown as a separate node, however the gsmSCFcould be co-located with any other node. Returning to FIG. 5 Similar asin the first approach in step 51, the HLR determines whether a nodesending a location update, supports MAGCF functionality. Thisdetermination might be performed by any preferably method, as it isdisclosed in the first approach. If the HLR determines that MAGCFfunction is not supported by the node sending Update Location, the HLRsends the CAMEL Trigger Detection Point for “Collect_Info” with anindication, which MAGCF currently serves the user and an address of theserving gsmSCF, step 51. Alternatively no address of the serving gsmSCFis sent and in this case any gsmSCF in the home network can becontacted. As already mentioned, if there is no serving MAGCF known inHLR, the HLR can use a predefined default MAGCF. In step 52 a call setuprequest is received in the serving MSC/VLR carrying the called B-number.When receiving said request the CAMEL Trigger Detection Point“Collect_Info” is triggered immediately, which leads that the MSC/VLRhalts call setup processing and contacts the gsmSCF as addressed by theCAMEL subscription data received from HLR. The CAP message InitialDP issent to the gsmSCF including the B-number and the indication of theserving MAGCF, step 53. The gsmSCF recognizes from the receivedindication, which MAGCF is currently serving the subscriber. Then thegsmSCF adds a prefix to the B-number, which is specific for that servingMAGCF. Preferably, the prefixes are predefined in the gsmSCF.

The gsmSCF then returns this modified B-number to the MSC/VLR andrequests to continue call setup to this new number. The CAP messageConnect is sent in step 54 from gsmSCF to MSC/VLR for this purpose. Bymeans of the received prefixed B-number, the serving MSC/VLR routes thecall to the MAGCF, step 55. The MAGCF receives the call coming in withthe prefixed B-number and removes the prefix. It is to be mentioned,that preferably also the A-number is to be provided by the MSC/VLR, inorder to allow the MAGCF to identify the right served subscriber. Instep 56, the call is routed to the S-CSCF of the A-subscriber forexecution of originating services. Here the B-number is again used ascalled destination.

Thus also the second approach ensures that all originating calls areprovided to the MAGCF serving a user.

In both approaches, when roaming in a network without support for MAGCFfunctionality, the last serving MAGCF is used as a roaming anchor.However, since the IMS AS is responsible for handling all services,service execution in the MSC/VLR has to be suppressed. Preferably amechanism to filter the subscriber data is proposed in order to preventthe MSC/VLR to handle any services. The HLR knows that a subscriber isroaming in a remote visited network. So when sending the MAP operationInsert Subscriber data, the HLR filters out all supplementary servicesubscriptions before sending the data to the MSC/VLR. Further it isproposed that when roaming in the home network, the subscriber data isnot filtered and the MAGCF takes care to suppress the any serviceinvocation. Another option is to filter the subscriber data also whensent in the home network to an MAGCF.

In the following a basic architecture for performing the originatingcall in the home network is presented in respect to FIG. 6. FIG. 6 showsa user A being the call originating user. Said user is connected over aradio access network, like UTRAN or GERAN to the MAGCF. Since the userperforms a call in the home network, it is directly connected to theMSC-S part of the MAGCF node. The IMS part of the MAGCF node conveys aconnection to the S-CSCF by means of the SIP protocol. In particular theintegrated P-CSCF knows the address of the S-CSCF. There is also the IMSAS node communicating with the S-CSCF.

The dotted lines depict the flow of signalling messages. In FIG. 6 alsoMGW and MRFP nodes are depicted, which are involved in the transmissionof user plane being indicated by the continuous lines.

According to FIG. 6 when the call request, step 61 is received in theMAGCF from the terminal, the MAGCF does not invoke any originatingservices and it also does not look at the received B-number. The MAGCFroutes the call to the IMS of the served subscriber. Since the P-CSCF inthe MAGCF still knows the S-CSCF from the IMS registration, the call isrouted straight to the S-CSCF, step 62. In step 63, the S-CSCF involvesthe IMS AS for invoking originating services and analysis of the dialedB-number. The checking of the originating services might for exampleinclude barring of all outgoing calls supplementary services, which forexample might be used when giving a phone to a third person then thebarring service might be activated in order to prohibit said user frommaking a call while still allowing him to be reachable for allterminating calls.

Further the MAGCF selects a MGW for handling the user plane. The IMS ASinvolves an MRFP for handling the user plane. MGW and MRFP arepreferably separate nodes.

In the following the message flow sequence for an originating call in aHome network is described in respect to FIG. 7. In FIG. 7 a calling userUE A originating a call to the called user B: IMS are depicted. Sincethe user performs a call in a home network by contacting the MSC-Sfunction integrated in the MAGCF node, therefore the MAGCF node with theMSC-S functionality is depicted. Further there is the A: S-CSCF, whichis the serving S-CSCF for the originating user, the A: IMS AS beingresponsible for the user. The lines depicted between two entitiesindicate flow of the messages and the arrows the direction of themessage exchange.

In the first step of a call originating procedure the calling user, UE Asends a 24.0008: CS Service Request to the MAGCF, in particular to theMSC-S. Said node performs at first a circuit-switched authentication forthe calling user as it is already known and in a subsequent step saiduser sends a 24.008: Setup message, which is confirmed by means of the24.008: Call Proceeding message. As aforementioned the MAGCF knows theaddress of the S-CSCF being responsible for the user and therefore saidaddress is taken to start the IMS Call setup procedure. In particularthe integrated P-CSCF knows the address of the S-CSCF. In the first stepSIP:Invite is sent to the S-CSCF serving the calling user A. Saidmessage includes as parameters the telephone number of the called userB, tel-URL and the Session Description Protocol Parameters of the user ASDP A. The SDP parameters are exchanged in the frame of SDP negotiationprocedure between the communication entities, which are the originatingand the terminating users. During the negotiation procedure mediacharacteristics, like for example number of media flows or codecs, arenegotiated.

Returning to FIG. 7 The A: S-CSCF sends a ISC:Invite (Tel-URL, SDP A) tothe A:IMS AS for invoking originating services and for analysing thedialled B-number. Upon receipt of an answer from the A:IMS AS, theA:S-CSCF sends a SIP:Invite (SIP-URL, SDP A) message to the terminatinguser, B:IMS. In a subsequent step the SDP negotiation procedure isstarted by sending the SIP:183 Session Progress (SDP B) carrying theproposed SDP parameters from the terminating user. Said message isforwarded to the MAGCF, which after contacting the responsible RAN(Radio Access Network), in order to check whether the proposed SDPparameters are supported and in order to reserve the resources requiredfor the negotiated session parameters. This is performed by means of themessages Assignment Request and Assignment Complete. In a following stepthe MAGCF sends a SIP:Update message through the A:S-CSCF to the B:IMS,which agrees on the new parameters by sending the SIP:200 OK (Update)message. In case, the called user is free and able to receive the call acorresponding indication, namely the SIP: 180 Ringing is sent to theMAGCF, which translates it into circuit-switched protocol besed message,namely 24.008:Alerting. After receiving the SIP:200OK (Invite) messagefrom the called user, B:IMS a 24.008: Connect message is sent to theoriginating user, UE A in order to finalize the establishment procedure.A confirmation of a successful performed call setup procedure is sent tothe terminating user by means of the 24.008: Connect Ack and SIP:Ackmessages. After successful performed call setup procedure a voice callmight be carried out.

In the following an embodiment is presented for performing anoriginating call in a remote visited network without support for MAGCFfunctionality. In this scenario, for a user roaming in this network, thelast serving MAGCF is used as a roaming anchor point. As described inthe previous embodiment, the HLR adds CAMEL data to the subscriber datawhen inserting subscriber data into the MSC/VLR, in order to enforcethat the call handling is performed in the anchor MAGCF. Thus, when acall request is received, the MSC/VLR notices the CAMEL data, whichcauses the call to be routed to the roaming anchor MAGCF. After the callhas reached the MAGCF, call setup continues as for the home networkcase, i.e. the call is forwarded to the S-CSCF for execution oforiginating services.

The originating call is presented in the following in more details inrespect to FIG. 9 presenting the flow of messages. The FIG. 9Corresponds to the FIG. 7 with the difference that in FIG. 9additionally the MSC/VLR located in the visited network is depicted.Further in FIG. 9 the MAGCF is depicted with the gsmSCF functionality.However this should not be seen as restriction. Alternatively the gsmSCFmight be provided as a separate node.

In the first step the user UE sends a 24.0008:CM Service Request messageto the MSC/VLR followed by a 24.008: Setup (B Number), which areconfirmed by the message 24.008: Call Processing. The receipt of themessages means for the MSC/VLR that the user wishes to establish aconnection to the user with the B-Number. However during theregistration procedure the MSC/VLR has received form the HLR a CAMELmessage, as described in the previous embodiments, informing that theuser is to be handled by the gsmSCF, Based on this information theMSC/VLR routes the call to the MAGCF over the gsmSCF. In the previousembodiment it is discussed how to route a call to a MAGCF. In thisparticular embodiment the routing by using a roaming number is shown.According to this approach the MSC/VLR has the address of the gsmSCF,which is also the address of the MAGCF. By means of this address theMAGCF is contacted, CAP: InitialDP(B-number). Upon receipt of thismessage the MAGCF performs a procedure for providing a routing number,which includes allocating of a roaming number and putting the allocatedroaming number in relation to the B-number. Said roaming number is sentto the MSC/VLR by means of the CAP:Connect (Roaming Number) message inorder to route the call by means of the roaming number, ISUP:IAM(Roaming Number). The rest of the procedure is similar to the stepsdescribed in respect to FIG. 7 leading to convey call originatingprocedure.

In the following embodiments describing a terminating call in the homenetwork in respect to FIG. 10 is described. The structure of the FIG. 10corresponds to the structure of FIG. 6. In step 101 the S-CSCF receivesa call which is to be terminated at the user B. The S-SCCF involves theIMS AS for execution of terminating services, step 102 and 103. Hereinthe terminating subscriber's services are checked, in a similar way asfor the originating case. For example the barring of all incoming callwhen roaming abroad might be activated. In this example IMS checkswhether a user has a subscription to this service, and then in case saiduser roams abroad, the call is blocked.

The S-CSCF knows the address of the serving MAGCF from the IMSregistration, as it is described in the above embodiments. In particularthe address of the integrated P-CSCF is known to the S-CSCF. By means ofa SIP protocol the call is forwarded to the MAGCF, in particular to theproxy gateway, P-CSCF located in the MAGCF, 104. The MAGCF terminatesthe call towards the terminal, however, without invocation of anyservice. The termination means that the IMS call is terminated in theMAGCF and converted to a CS call which is then forwarded for example bymeans of a 24.0008 protocol to the B user over an Access Network, likefor example UTRAN or GERAN, 105. The described call terminating routingis preferably restricted to the routing of signaling information. It isproposed that the payload information is routed on a direct way via MRFPand MGW to the Access Network, as it is depicted in FIG. 6 by means ofthe continuous line.

The flow of messages for call terminating procedure is presented in thefollowing in respect to FIG. 11. FIG. 11 shows an IMS user, A:IMSwishing to be connected to the user B, UE B. In a first step the I-CSCFis contacted which is responsible within an operator's network for allconnections destined to a subscriber of that network operator, or aroaming user currently located within that network operator's servicearea. The contacting is performed by means of SIP:Invite (SIP URL, SDPA). Multiple I-CSCFs within an operator's network might be available.The main function performed by the I-CSCF is assigning a S-CSCF to auser performing SIP registration. According to the present invention theS-CSCF knows the address of the MAGCF and in particular of the P-CSCFintegrated in the MAGCF and therefore the SIP:Invite might be forwardedto the MAGCF. In respect to FIG. 11 before forwarding the message to theMAGCF, the B:IMS AS is contacted by means of the ISC:Invite messages inorder to terminate the IMS services. Upon receipt of theSIP:Invite(SIP-URL, SDP A) the IMS call is terminated in the MAGCF and acircuited-switched handling is initiated, including sending the 24.008:Paging message to the called user, UE B, performing thecircuited-switched authentication, and establishing a call to the UE Bby means of the 24.008: Call Setup and 24.008:Call Confirmed messages.The rest of the procedure is similar to the procedure described inrespect to FIG. 7. This means that the IMS part located in the MAGCF,namely the P-CSCF sends a SIP: 183 Session Progress (SDP B) message tothe A:IMS user with the proposed parameters. According to the FIG. 11 anupdate of the parameters at both communicating sides is performed bymeans of the SIP:Update and SIP:200OK messages. Upon the parameters areassigned, a ringing signal occurs, 24.008: Alerting, SIP:180 Ringing,and a connecting procedure, 24.008: Connect, SIP:200OK(invite) with theconfirmation messages, SIP:ACK and 24.008: Connect ACK is performed.

Of course it might happen that the calling user is located in a visitednetwork, B visited, without MAGCF functionality. This scenario isdescribed in the following in respect to FIG. 12 showing the terminatingcall for user B. In this case the IMS part of a call is to be terminatedin a MAGCF being responsible for the user and acting as a roaminganchor. Thus, the terminating call is routed to the S-CSCF, 121, whichthen involves the IMS AS for execution of terminating services, 122 and123. As already mentioned the S-CSCF knows the address of the servingMAGCF from the IMS registration. Thus, the call is transmitted,preferably by means of the SIP protocol to the MAGCF, 124. Said MAGCFrecognizes that it works as a roaming anchor, thus when the terminatingcall is received in the MAGCF, the MAGCF recognizes that it cannotterminate the call directly, but has to involve the serving MSC/VLR. Sothe MAGCF acts as a GMSC and asks the HLR for routing information. TheHLR fetches the roaming number from the serving MSC/VLR, 126 and returnsit to the MAGCF, 125. The call is then routed from the MAGCF to theMSC/VLR using the roaming number, 127. It is to be noted that noservices are executed in the HLR, since for the execution of saidservices the IMS AS is responsible. The signaling sequence is similar tothe sequence described in respect to FIG. 11 with the difference that acorresponding signaling, preferably MAP based signaling is to beexchanged between the MAGCF, HLR and MSC/VLR, wherein said MSC/VLR isresponsible for establishing a connection to the user B.

The above-described embodiments are based on integration ofcellular-switched controlled users equipment, like it is provided in GSMor GPRS, into IMS services developed in connection with UMTS. However,the present invention is not only restricted to these networks. Afurther example might be CDMA2000 providing corresponding nodes as thenodes existing in GPRS or UMTS.

1. Access Gateway Node (MAGCF) adapted to handle a call in apacket-based multimedia system (IMS) domain for a circuit-switchedcontrolled user's terminal (MS) located in circuit-switched controlleddomain (CS) wherein said Access Gateway Node (MAGCF) comprises anoriginating circuit-switched logic (Org CS) adapted to receive anoriginating circuit-switched call either directly from thecircuit-switched controlled user's terminal (MS) or from a servingmobile circuit-switched function serving mobile circuit-switchedfunction by means of a routing number being used to route thecircuit-switched call to the Access Gateway Node (MAGCF) and, anoriginating packet-based multimedia logic (Org PS) adapted to send anoriginating packet-based multimedia call via a proxy call controlfunction (P-CSCF) being part of the Access Gateway Node (MAGCF) towardsthe packet-based multimedia domain (IMS), and a terminating packet-basedmultimedia logic (Term PS) adapted to receive from the packet-basedmultimedia domain (IMS) a terminating packet-based multimedia call beingaddressed to the proxy call control function (P-CSCF) being part of theAccess Gateway Node (MAGCF), and a terminating circuit-switched logic(Term CS) adapted to send a terminating circuit-switched call towardsthe circuit-switched controlled user's terminal, and a conversionfunction (Conv) adapted to convert the originating circuit-switched callinto the originating packet-based multimedia call and the terminatingpacket-based multimedia call into the terminating circuit-switched call.2. Access Gateway Node (MAGCF) according to claim 1 wherein the routingnumber is an address of a dialled user modified with routing informationto route the call to the Access Gateway Node serving the user.
 3. AccessGateway Node (MAGCF) according to claim 1 wherein the routing number isa temporary roaming address assigned to the call for routing the call tothe Access Gateway Node serving the user.
 4. Access Gateway Node (MAGCF)according to claim 2 or 3 wherein the routing number is assignedaccording to an indication about the Access Gateway Node serving theuser received from a user's directory located in the circuit-switcheddomain.
 5. Access Gateway Node (MAGCF) according to claim 1 wherein theterminating circuit-switched logic is adapted to send a terminatingcircuit-switched call to the user in case a serving circuit-switchednode is part of the circuit-switched function or to send to the servingcircuit-switched node in case said serving circuit-switched node is nota part of the circuit-switched function.
 6. Access Gateway Node (MAGCF)according to claim 1 wherein said Access Gateway Node comprises aregistration logic adapted to perform a registration procedure of thecircuited-switched controlled user in the packet-based multimediadomain, wherein said registration procedure results in storing anaddress of a serving packet-based multimedia node in the Access GatewayNode and in providing an address of the Access Gateway Node to theserving packet-based multimedia node.
 7. Access Gateway Node (MAGCF)according to claim 6 wherein the provision of the address of the AccessGateway Node is the provision of the proxy call control function. 8.Access Gateway Node (MAGCF) according to claim 1 wherein the AccessGateway Node comprises a suppression function adapted to suppress thereceived originating circuited-switched call from handling in thecircuit-switched domain.
 9. Access Gateway Node (MAGCF) according toclaim 1 wherein the Access Gateway Node comprises a termination functionadapted to terminate the received terminating packet-based multimediacall.
 10. Method for handling a call for a circuit-switched controlleduser's terminal (MS) located in circuit-switched controlled domain (CS)wherein said call is to be handled in a packet-based multimedia domain(IMS) with the following steps performed in said Access Gateway Node(MAGCF) Performing call originating procedure comprising Receiving anoriginating circuit-switched call either directly from thecircuit-switched controlled user's terminal or from a serving mobilecircuit-switched function by means of a routing number being used toroute the circuit-switched call to the Access Gateway Node (MAGCF)(20,21) and, Converting the originating circuit-switched call into anoriginating packet-based multimedia call (22) and, Sending theoriginating packet-based multimedia call via an integrated proxy callcontrol function towards the packet-based multimedia domain (23) and,Performing call terminating procedure comprising Receiving from thepacket-based multimedia domain a terminating packet-based multimediacall being addressed to the integrated proxy call control function(30,31) and, Converting the terminating packet-based multimedia callinto a terminating circuit-switched call (32) and, Sending theterminating circuit-switched call towards the circuit-switchedcontrolled user's terminal (33).
 11. Method according to claim 10wherein the routing number is an address of a dialled user modified withrouting information to route the call to the Access Gateway Node servingthe user.
 12. Method according to claim 10 wherein the routing number isa temporary roaming address assigned to the call for routing the call tothe Access Gateway Node serving the user.
 13. Method according to claim11 or 12 wherein the routing number is assigned according to anindication about the Access Gateway Node serving the user received froma user's directory located in the circuit-switched domain.
 14. Methodaccording to claim 10 wherein the received originatingcircuited-switched call is suppressed in the Access Gateway Node fromhandling in the circuit-switched domain.
 15. Method according to claim10 wherein to terminate the received terminating packet-based multimediacall is terminated in the Access Gateway Node.